1. Field of the Invention
The present invention relates to signal processing techniques. In particular, the present invention relates to estimating Doppler spread and signal-to-noise ratio (SNR) of a received signal.
2. Discussion of the Related Art
In many communication systems, the received signal often includes a training sequence or a pilot subcarrier. For example, DVB-T/H OFDM signals are examples of such signals. In such systems, it is desirable to estimate both the Doppler spread and SNR of the received signal. The estimated Doppler spread and SNR are used to select optimum values of reception and demodulation parameters that accommodate channel conditions change.
In an article by David R. Pauluzzi, “A Comparison of SNR Estimation Techniques for the AWGN Channel”, IEEE Transactions on Communications; Vol. 48, No. 10, pp. 1681-1691 (Oct. 2000), numerous methods for estimating the SNR of single-carrier signals in additive white Gaussian noise (AWGN) channels are discussed. These methods can be extended to estimate the SNR of an OFDM signal by treating the OFDM signal as a collection of single-channel signals. Likewise, some of these methods may be extended to estimate the SNR in Rayleigh fading channels, using an appropriately small time interval to estimate the signal statistics. The split-symbol moment estimator is particularly suited for this approach. See, e.g., S. K. Simon and A. Mileant, “SNR Estimation for the Baseband Assembly”; Telecommunications and Data Acquisition Prog. Rep. 42-85 Jet Propulsion Lab., Pasadena, Calif. (May 15, 1986); and B. Shah and S. Hinedi, “The Split Symbol Moments SNR Estimator in Narrowband Channels”; IEEE Transactions on Aerospace Electronic Systems; Vol. AES-26, pp. 737-747 (September 1990). U.S. Pat. No. 6,922,452 to Sandberg describes a method for estimating Doppler spread on a single-channel signal by computing the autocorrelation of the received signal and relating its first zero-crossing to the Doppler spread bandwidth. While this method could be applied to individual subcarriers of an OFDM signal, the computation and storage requirements are excessive for a mobile receiver that must consume a minimum of power.